v0.8.99

nv2a: Ignore alpha when processing PVIDEO color keying

Discards the alpha value passed to the color key register, matching tested
hardware behavior.

Fixes #2421

Tests: https://github.com/abaire/nxdk_pgraph_tests/blob/c64f5af5f7c3a890f1a00a927c6b72c2656ea025/src/tests/pvideo_tests.cpp#L761

Note: PVIDEO tests do not produce artifacts so they must be compared manually
against HW. I have verified that they are identical for the subset of surface
formats supported by xemu.